A folding apparatus of this general type is known from DE 44 12 142 C2. This prior art device comprises a collecting cylinder, a folding jaw cylinder and a cutting unit which is located upstream of the collecting cylinder. The cutting unit is used to divide the web of material into the individual products. The collecting cylinder has a plurality of grippers to which the leading edge of a product is fed. The grippers press this leading edge of each such cut, individual product against the collecting cylinder, which will convey it further. To allow the grippers to pivot between a released position and a holding position, without damaging the products, the products must be offset from each other around the periphery of the collecting cylinder by an intermediate space in which the grippers are able to move. To provide this intermediate space, the peripheral speed of the collecting cylinder must be greater than the speed at which the web of material is fed into the folding apparatus.
The collecting cylinder described in DE 44 12 142 C2 is also equipped with a plurality of folding blades, which, when the folding apparatus is in fold production mode, extend each time they pass through a gap that is formed between collecting cylinder and folding jaw cylinder. Each of these folding blades press products that lie in front of them into a folding jaw of the folding jaw cylinder. The first cross fold, which is produced in this manner, is intended to divide the products at the center. It is thus necessary, when processing products of different lengths, to be able to vary the distance between grippers and folding blades on the collecting cylinder. To accomplish this result, grippers and folding blades are mounted on two different nested parts of the collecting cylinder, which two parts can be rotated counter to one another.
In fold production mode, the folding blades of the collecting cylinder must always meet with the folding jaws of the folding jaw cylinder at a transfer gap that is formed between the collecting cylinder and the folding jaw cylinder, in order to insert a product into the folding jaws of the folding jaw cylinder. The part of the collecting cylinder that holds the folding blades is therefore rigidly rotatably coupled to the folding jaw cylinder.
In book production mode, each of the grippers of the collecting cylinder passes through the transfer gap at the same time as does a gripper of the folding jaw cylinder. During such passage through the transfer gap, the gripper of the collecting cylinder pivots from a product end holding position to a product end released position. At the same time, the gripper of the folding jaw cylinder pivots from the released position to the holding position. A product is thus transferred from the collecting cylinder to the folding jaw cylinder without being cross folded, especially if the folding blades are also deactivated.
A circumferential distance between grippers and folding blades on the collecting cylinder is adjustable. The folding blades and the folding jaws must always pass through the transfer gap simultaneously, regardless of variations of this circumferential distance between grippers and folding blades on the collecting cylinder. As a result, the grippers of the collecting cylinder and those of the folding jaw cylinder are able to pass through the gap at different times. If a gripper of the folding jaw cylinder strikes a product, while that gripper is passing through the gap, the product will be damaged as a result of a pivoting movement of this gripper. To prevent this product damage, the gripper of the folding jaw cylinder must always strike an intermediate space on the collecting cylinder, between the products which are held on the collecting cylinder. For this reason, an angular distance between the grippers and the folding jaws of the folding jaw cylinder is chosen such that, when the distance between a gripper of the collecting cylinder and a gripper on the folding blade, that is interacting with a product being held by this gripper of the collecting cylinder is set to the greatest possible value, the grippers of the collecting cylinder and those of the folding jaw cylinder will pass through the gap between the two cylinders simultaneously. If the angular distance is adjusted to be smaller, the gripper of the folding jaw cylinder passes through the gap shortly before the gripper of the collecting cylinder. The gripper of the folding jaw cylinder can thus be prevented from colliding with a product on the collecting cylinder, as long as the intermediate space between the products on the collecting cylinder is large enough.
The intermediate space which is required for this purpose must be wider than the width of a space that is necessary merely to extend the grippers of the collecting cylinder. Its width typically measures approximately 6 cm. Assuming that each of the products is 50 cm in length, it follows that, to generate the necessary intermediate space, the speed at which the web of material is fed to the cutting unit must be 12% slower than the peripheral speed of the cylinders. However, the latter speed is limited due to the centrifugal forces that occur during revolution of the cylinders. Thus, the wider the required intermediate space, the slower the web must be fed in, and the lower is the resulting productivity. The shorter the products are, the less favorable is the ratio of web infeed rate to peripheral speed of the cylinders.
DE 43 42 037 C1 and DE 36 28 411 A1 both disclose folding apparatuses having variable cut-off lengths.